Bluetooth: Controller: Fix assertion failed [evdone]

When there are radio events with time reservations lower
than the preemption timeout of 1.5 ms, the pipeline has to
account for the maximum radio events that can be enqueued
during the preempt timeout duration. All these enqueued
events could be aborted in case of late scheduling needing
as many done event buffers.

During continuous scanning, there can be 1 active radio
event, 1 scan resume and 1 new scan prepare. If there are
peripheral prepares in addition, and due to late scheduling
all these will abort needing 4 done buffers.

If Extended Scanning is supported, then an additional
auxiliary scan event's prepare could be enqueued in the
pipeline during the preemption duration.

Fixes #36381.

Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: cvinayak

subsys/bluetooth/controller/ll_sw/ull.c

@@ -305,10 +305,31 @@ static MFIFO_DEFINE(prep, sizeof(struct lll_event), EVENT_PIPELINE_MAX);
 
 /* Declare done-event FIFO: mfifo_done.
  * Queue of pointers to struct node_rx_event_done.
- * The actual backing behind these pointers is mem_done
+ * The actual backing behind these pointers is mem_done.
+ *
+ * When there are radio events with time reservations lower than the preemption
+ * timeout of 1.5 ms, the pipeline has to account for the maximum radio events
+ * that can be enqueued during the preempt timeout duration. All these enqueued
+ * events could be aborted in case of late scheduling, needing as many done
+ * event buffers.
+ *
+ * During continuous scanning, there can be 1 active radio event, 1 scan resume
+ * and 1 new scan prepare. If there are peripheral prepares in addition, and due
+ * to late scheduling all these will abort needing 4 done buffers.
+ *
+ * If there are additional peripheral prepares enqueued, which are apart by
+ * their time reservations, these are not yet late and hence no more additional
+ * done buffers are needed.
+ *
+ * If Extended Scanning is supported, then an additional auxiliary scan event's
+ * prepare could be enqueued in the pipeline during the preemption duration.
  */
 #if !defined(VENDOR_EVENT_DONE_MAX)
-#define EVENT_DONE_MAX 3
+#if defined(CONFIG_BT_CTLR_ADV_EXT) && defined(CONFIG_BT_OBSERVER)
+#define EVENT_DONE_MAX 5
+#else /* !CONFIG_BT_CTLR_ADV_EXT || !CONFIG_BT_OBSERVER */
+#define EVENT_DONE_MAX 4
+#endif /* !CONFIG_BT_CTLR_ADV_EXT || !CONFIG_BT_OBSERVER */
 #else
 #define EVENT_DONE_MAX VENDOR_EVENT_DONE_MAX
 #endif